: My 94 seville idles and runs terrible. I've done everything!

06-13-06, 02:56 PM
Help! Please! I have a 94' Seville SLS with a 4.6L N* (88K). The car is in great shape but for the last month it's been running terrible. When the engine is warm it stumbles and lurches at idle and in gear. It's worse when the engine has more load - like the AC is on. I don't have any codes showing but I do get the "service engine soon" light. The engine temperature ranges from 212 to 230. I've cleaned the throttle body, changed the fuel filter, replaced the Crankshaft sensors, replaced the MAP Sensor, cleaned and Inspected the ECR, changed the Plugs, replaced the Ignition Control Module (not the coils) and took it to two different dealerships (they didn't know what to do either). I'm about to replace the ignition coils and the spark plug cables. Still no codes. Does anybody have any ideas before I replace the whole engine piece by piece? (or drive it into the bay)

06-13-06, 03:37 PM
mine does the same thing and it is making me really mad. I have no clue what it is, if i cant figure it out im going to take it to a mechanic.

06-13-06, 03:52 PM
I don't have any codes showing but I do get the "service engine soon" light.

That would be a problem. Any time the SES light comes on, there is a code stored. If there is no code stored, one has to look at the PCM with suspicion.

However, I think you might be holding back some history codes, aren't you?

06-13-06, 07:46 PM
I would suspect plug wires
so easy to do its a shame none of the dealers
have suggested this.
ECM thats flaky will also drive you crazy.
Do you know what ECM you have(4 letter code)

06-13-06, 09:25 PM
Eldo1 is right. A DTC sets the SES light. If you have the SES light on, then there has to be a DTC set.

Change the plug wires. Check the FPR. Put a fuel pressure guage on the fuel rail and get a pressure reading when it is acting up.

06-14-06, 08:26 PM
OK, I just changed the spark plug cables. It runs a little better but still not the problem! Eldo1 asked for history codes - here it is: PO25 - 24X reference signal low. What on earth does that mean?:rant2:

06-14-06, 09:32 PM
That's better. :p

It means, your 24x reference signal from your ignition module isn't making it to the PCM. Replacing the module eliminates that as a possibility. Are you comfortable using a multimeter? There are some tests you can do with one to check whether it's a wiring issue, or a PCM issue.

There was someone having similar problems a few weeks ago that traced it to the PCM. You might want to do a search to see if you can find it.

This thread:

Although last i heard it might not have fixed the problem. Not sure..

06-15-06, 08:06 AM
OK. I was leaving the PCM for last. I guess I need to head to a junkyard this Saturday. They mentioned in the "Northstar barely running" post a serial number. That the serial numbers on the PCMs should match. Does anyone have any details about this?

06-15-06, 09:22 AM
there's a "service number" on the sticker that needs to be the same.

06-15-06, 07:03 PM
again do you know the 4 letter code of your PCM?

06-16-06, 08:37 AM
No, at the moment, I don't know the 4 letter code. I went looking for the PCM last night and was surprised to find it under the dash. My Haynes manual says that the 4.6L PCM is under the Air Filter. Parts68 - you are asking for the code like you know something the rest of us don't. Please share. Thanks for the help.

06-16-06, 06:21 PM
Ok, here's the four letter code - BHMP. What's up?

06-16-06, 08:42 PM
Ill check on the couple spares I have and see if its a match.
I think you can use the PCM and swap out your memcal,should do the trick.
But never can tell if problem is in memcal.
99% of time is the PCM not memcal.

06-23-06, 10:02 AM
Here's the latest. It's still not fixed. After searching junkyards, I finally found a new (used) PCM with the same service code. But, the engine missing and surging are still there. Code 025, 24x reference signal low. I'm starting to check all the wiring. Here's an interesting note - I disconnected the plug from the Camshaft sensor to the ICM and the car started running great. Is this because the Camshaft sensor is bad or is the PCM switching to "limp" mode? Also my battery died in the process of this latest round of fixes. Does that mean anything or was it a coincidence? :confused:



06-23-06, 01:07 PM
Well then, you've got either an open or a short to ground on your 24x reference line. This starts at pin "A" on the large connecter nearest the 5/2 coil, and ends at "F1" on the blue PCM connector. The wire color is light blue with a black stripe. Check for continuity between those two points. Then check to see (with both ends unplugged) if it is shorted to ground.